# Second Harmonic - Standing Waves

1. Sep 10, 2011

### Peter G.

Hi,

Question: Describe how you would arrange for a string that is et under tension, with both ends fixed, to vibrate in its second harmonic mode.

Ok, the string has a speed, v, and wavelength, w, which give it a fundamental frequency, f. If we want the second harmonic, we have to change the frequency so that a full wave fits the length of the string. So in this case we would need twice the frequency, or half the wavelength.

I think this is how you would do it but, as you can see, I am still a bit confused. How could I formally answer this question?

Thanks,
Peter G.

2. Sep 10, 2011

### kuruman

You would formally answer the question just like you did. "Drive the string with a frequency that is twice the first harmonic or twice the fundamental frequency."

3. Sep 10, 2011

### Peter G.

Ok, cool. Just one more question (I hope it is not too general): I don't understand how resonance comes into Standing Waves...

4. Sep 10, 2011

### kuruman

Suppose you have a string of fixed length under fixed tension and you have a waveform generator that you can use to drive the string at the frequency of your choice. If you match the driving frequency to one of the harmonics, then you get a standing wave. Otherwise you don't. The frequencies that create the standing waves are the "resonant" frequencies.

5. Sep 10, 2011

### Peter G.

Ah ok, got it! Thanks a lot!

6. Sep 17, 2011

### Petit Einstein

Can u help me to more understand about standing wave?

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